A Hydrogen vehicle is a vehicle, such as an automobile, aircraft, or any other kind of vehicle that uses hydrogen as its primary source of power for locomotion. These vehicles generally use the hydrogen in one of two methods: combustion or fuel-cell conversion:

* In combustion, the hydrogen is "burned" in engines in fundamentally the same method as traditional gasoline cars.
* In fuel-cell conversion, the hydrogen is reacted with oxygen to produce water and electricity, the latter of which is used to power electric motors.Hydrogen can be obtained through various thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called thermolysis, or as a microbial waste product called biohydrogen or Biological hydrogen production. Hydrogen can also be produced from water by electrolysis. If the electricity used for the electrolysis is produced using renewable energy, the production of the hydrogen would (in principle) result in no net carbon dioxide emissions.

A potential benefit of using hydrogen as an energy carrier in vehicles is that, theoretically, the source of pollution created today by burning fossil fuels could be moved to centralized power plants, where the byproducts of burning fossil
fuels can be better controlled. However, there are both technical and economic challenges to implementing wide-scale use of hydrogen vehicles, and the timeframe in which such challenges may be overcome is likely to be at least several decades.

At a panel of scientists, engineers and industry experts that the National Academy of Sciences assembled in April 2007 to review the president's $1.2 billion "hydrogen initiative," panelists agreed that President Bush's hydrogen car goals are slipping away. According to physicist and former U.S. Department of Energy official Joseph Romm, for example, "A hydrogen car is one of the least efficient, most expensive ways to reduce greenhouse gases." Asked when hydrogen cars will be broadly available, Romm replied: "Not in our lifetime, and very possibly never." General Motors disagrees with that sentiment and has announced that it will start hydrogen vehicle production in 2010. However, GM's chief engineer on the fuel cell project, Mohsen Shabana, said hydrogen infra-structure would not be in place by then, and he noted that GM had produced only two test units of the Sequel (pictured above) so far.


Research and prototypes

Hydrogen does not come as a pre-existing source of energy like fossil fuels, but rather as a carrier, much like a battery. It can be made from both renewable and non-renewable energy sources. A potential advantage of hydrogen is that it could be produced and consumed continuously, using solar, water, wind and nuclear power for electrolysis. Currently, however, hydrogen vehicles utilizing hydrogen produced using hydrocarbons, produce more pollution than vehicles consuming gasoline, diesel, or methane in a modern internal combustion engine, and far more than plug-in hybrid electric vehicles. This is because, although hydrogen fuel cells generate less CO2 than conventional internal combustion engines, production of the hydrogen creates additional emissions. While methods of hydrogen production that do not use fossil fuel would be more sustainable,currently such production is not economically feasible, and diversion of renewable energy (which represents only 2% of energy generated) to the production of hydrogen for transportation applications is inadvisable.

The recorded number of hydrogen-powered public vehicles in the United States was 200 as of April 2007, mostly in California, and a significant amount of research is underway to try to make the technology viable. The common internal combustion engine, usually fueled with gasoline (petrol) or diesel liquids, can be converted to run on gaseous hydrogen. However, the more
energy efficient use of hydrogen involves the use of fuel cells and electric motors instead of a traditional engine. Hydrogen reacts with oxygen inside the fuel cells, which produces electricity to power the motors. One primary area of research is hydrogen storage, to try to increase the range of hydrogen vehicles, while reducing the weight, energy consumption, and complexity of the storage systems. Two primary methods of storage are metal hydrides and compression.

High-speed cars, buses, submarines, airplanes and rockets already can run on hydrogen, in various forms at great expense. NASA uses hydrogen to launch Space Shuttles into space. There is even a working toy model car that runs on solar power, using a reversible fuel cell to store energy in the form of hydrogen and oxygen gas. It can then convert the fuel back into water to release the solar energy.

Hydrogen fuel cell difficulties

While fuel cells themselves are potentially highly energy efficient, and working prototypes were made by Roger E. Billings in the 1960s, at least four technical obstacles and other political considerations exist regarding the development and use of a fuel cell-powered hydrogen car.
Low volumetric energy

Hydrogen has a very low volumetric energy density at ambient conditions, equal to about one-third that of methane. Even when the fuel is stored as a liquid in a cryogenic tank or in a pressurized tank, the volumetric energy density (megajoules per liter) is small relative to that of gasoline. Because of the energy required to compress or liquefy the hydrogen gas, the supply chain for hydrogen has lower well-to-tank efficiency compared to gasoline. Some research has been done into using special crystalline materials to store hydrogen at greater densities and at lower pressures.

Instead of storing molecular hydrogen on-board, some have suggested that using hydrogen reformers to extract the hydrogen from more traditional fuels including methane, gasoline, and ethanol, or using reformed gasoline or ethanol to power fuel cells.[citation needed] However, using gasoline for this purpose would promote continued dependence on fossil fuels.

Fuel cell cost

Currently, hydrogen fuel cells are costly to produce and fragile. Scientists are studying how to produce inexpensive fuel cells that are robust enough to survive the bumps and vibrations that all automobiles experience. Also, many designs require rare substances such as platinum as a catalyst in order to work properly. Such a catalyst can also become contaminated by impurities in the hydrogen supply. In the past few years, however, a nickel-tin catalyst has been under development which may lower the cost of cells.

Fuel cells are generally priced in USD/kW, and data is scarce regarding costs. Producer Ballard is virtually alone in publishing such data. Their 2005 figure was $73 USD/kW (based on high volume manufacturing estimates), which they said was on track to achieve the U.S. DoE's 2010 goal of $30 USD/kW. This would achieve closer parity with internal combustion engines for automotive applications, allowing a 100 kW fuel cell to be produced for $3000. 100 kW is about 134 hp.

Freezing conditions

Freezing conditions are a major consideration because fuel cells produce water and utilize moist air with varying water content. Most fuel cell designs are fragile and can't survive in such environments at startup but since heat is a byproduct of the fuel cell process, the major concern is startup capability. Ballard announced that it has already hit the U.S. DoE's 2010 target for cold weather starting which was 50% power achieved in 30 seconds at -20 °C.

Hydrogen production cost

Chemically pure hydrogen is derived from a feed stock, such as methanol, but can also be produced from water. Current technologies use between 165% to 212% of the higher heating value to produce hydrogen. The energy to drive this conversion can be produced from fossil fuels, or renewable energy sources. The production of hydrogen from methanol as a feed stock or by using fossil fuels creates emissions of greenhouse gases, whereas production using renewable sources would not create such emissions. However, hydroelectricity accounts for approximately 6% of the energy produced worldwide, while other renewable resources, such as geothermal, solar and wind consisted of only about 1.4% of energy production as of 2004. Development of renewable sources faces barriers, and although the amount of energy produced from renewable sources is increasing, as a percentage of worldwide energy production, renewables decreased from 8.15% in 2000 to 7.64% of total energy production in 2004 due to the rapid increase in coal and natural gas production. However, in some countries, hydrogen is being produced using renewable sources. For example, Iceland is using geothermal power to produce hydrogen, and Denmark is using wind.

The conversion of feed stock to produce hydrogen has inherent losses of energy that make hydrogen less advantageous as an energy carrier. Additionally, there are economic and energy penalties associated with packaging, distribution, storage and transfer of hydrogen. Hydrogen fuel cells are theoretically (without auxiliary devices to run the fuel cell) more efficient than internal combustion engines, achieving efficiencies of 50-60%, making up much of what is lost in producing hydrogen, and produce only water out the tailpipe, mostly in the form of water vapor.

Hydrogen infrastructure

In order to distribute hydrogen to cars, the current gasoline fueling system would need to be replaced, or at least significantly supplemented with hydrogen fuel stations. Hydrogen stations are being built in various places around the world. Private and state initiatives like California's "California Hydrogen Highway" are already starting the infrastructure transition in advance of any manufacturers mass producing hydrogen cars. Replacement of the existing extensive gasoline fuel station infrastructure would cost a half trillion U.S. dollars in the United States alone.

Service life

Although service life is coupled to cost, fuel cells have to be compared to existing machines with a service life in excess of 5000 hours. As of today, however, no medium or low temperature fuel cells have been tested for more than two thousand hours.

Political considerations

Since all energy sources have drawbacks, a shift into hydrogen-powered vehicles may require difficult political decisions on how to produce this energy. The United States Department of Energy has already announced a plan to produce hydrogen directly from generation IV reactors. These nuclear power plants would be capable of producing hydrogen and electricity at the same
time. The main problem with the nuclear-to-hydrogen economy is that hydrogen is ultimately only an energy carrier. The costs associated with electrolysis and transportation and storage of hydrogen may make this method uneconomical in comparison to direct utilization of electricity. Electric power transmission is about 95% efficient and the infrastructure is already in place, so tackling the current drawbacks of electric cars or plug-in hybrid electric vehicles may be easier than developing a whole new hydrogen infrastructure that mimics the obsolete model of oil distribution. Continuing research on cheaper, higher capacity batteries is needed for the direct electric alternative to be practical. Direct transmission through electric rails, for example in a guided vehicle configuration such as personal rapid transit, may turn out to make electric vehicles more economic than hydrogen fuel cell vehicles. As a 2007 article in Technology Review argued,

In the context of the overall energy economy, a car like the BMW Hydrogen 7 would proba­bly produce far more carbon dioxide emissions than gasoline-powered cars available today. And changing this calculation would take multiple breakthroughs--which study after study has predicted will take decades, if they arrive at all. In fact, the Hydrogen 7 and its hydrogen-fuel-cell cousins are, in many ways, simply flashy distractions produced by automakers who should be taking stronger immediate action to reduce the greenhouse-gas emissions of their cars.

Recently, alternative methods of creating hydrogen directly from sunlight and water through a metallic catalyst have been announced. This may eventually provide an economical, direct conversion of solar energy into hydrogen, a very clean solution for hydrogen production. United States President George W. Bush was optimistic that these problems could be overcome with research. In his 2003 State of the Union address, he announced the which complements the President's existing FreedomCAR initiative for safe and cheap hydrogen fuel cell vehicles. Critics charge that focus on the use of the hydrogen car is a dangerous detour from more readily available solutions to reducing the use of fossil fuels in vehicles.

Alternatives

A 2006 article, "Hybrid Vehicles Gain Traction", in Scientific American (April 2006), co-authored by Joseph J. Romm and Prof. Andrew A. Frank, argues that hybrid cars that can be plugged into the electric grid (Plug-in hybrid electric vehicles), rather than hydrogen fuel-cell vehicles, will soon become standard in the automobile industry. To achieve lower emission goals, the power grid re-charging these vehicles will need to contribute significantly less emissions and wean themselves from fossil fuels for energy conversion. Battery electric vehicles, such as the General Motors EV1 typically have four times the efficiency of hydrogen vehicles, when the cost of producing hydrogen is included, and are gaining popularity, particularly with the introduction of new models like the Tesla.

Hydrogen internal combustion

Hydrogen internal combustion engine cars are different from hydrogen fuel cell cars. The hydrogen internal combustion car is a slightly modified version of the traditional gasoline internal combustion engine car. These hydrogen engines burn fuel in the same manner that gasoline engines do. As in hydrogen fuel cell vehicles, the volume of the vehicle that the tank occupies is significant. Research is underway to increase the amount of hydrogen that can be stored onboard, be it through high pressure hydrogen, cryogenic liquid hydrogen, or metal hydrides.In 1807, François Isaac de Rivaz built the first hydrogen-fueled internal combustion vehicle. However, the design was very unsuccessful. It is estimated that more than a thousand hydrogen-powered vehicles were produced in Germany before the end of the World War II prompted by the acute shortage of oil.

BMW's CleanEnergy internal combustion hydrogen car has more power and is faster than hydrogen fuel cell electric cars. A BMW hydrogen car (BMW H2R) broke the speed record for hydrogen cars at 186 mi/h (300 km/h), and BMW has an even newer Hydrogen 7 model. Mazda has developed Wankel engines to burn hydrogen. The Wankel engine uses a rotary principle of operation, so the hydrogen burns in a different part of the engine from the intake. This reduces intake backfiring, a risk with hydrogen-fueled piston engines. However the major car companies like DaimlerChrysler and General Motors Corp, are investing in the more efficient hydrogen fuel cells instead. Ford Motor Company is investing in both fuel cell and hydrogen internal combustion engine research. Because of the large heat exchanger necessary for fuel cells and their limited load change and cold start capability, they are certainly first choice as range extender for battery electric vehicles. The Wall Street Journal, reviewing BMW's new internal combustion hydrogen vehicle concluded: A more efficient route for car makers would be to focus
on high-mileage gasoline-powered vehicles. They are far simpler and less sexy than hydrogen cars... but for now they stack up as the cleaner option.

Outside of specialty and small-scale uses, the primary target for the widespread application of fuel cells (hydrogen, zinc, other) is the transportation sector; however, to be economically and environmentally feasible, any fuel cell based engine would need to be more efficient from wellhead-to-wheel, than what currently exists.

Fuel stations

Since the turn of the millennium, filling stations offering hydrogen have been opening worldwide. However, this does not begin to replace the existing extensive gasoline fuel station infrastructure, which would cost a half trillion U.S. dollars in the United States alone.

Planes

Many companies such as Boeing and Smartfish are pursuing hydrogen as fuel for planes. Unmanned hydrogen planes have been tested and Boeing is currently planning a manned flight for 2008.